As used herein, the term "fiber" includes fibers of extreme or indefinite length (i.e., filaments) and fibers of short length (i.e., staple fibers). The term "yarn" as used herein means a continuous strand of fibers.
The terms "stain" and "staining" as used herein with reference to polyamide fibers mean discoloration of such fibers caused by a chemical or physical attraction thereof with a substance such as, for example, food red. The terms "stain-resistant" and "stain resistance" as used herein with respect to polyamide fibers or carpets refers to the ability of the fiber or carpet to resist staining.
As used herein, "unmodified polyamide" refers to a typical commercially available polyamide with an AEG above 20 meq/kg that is known in the art such as, for example, nylon 6 or nylon 6,6.
Polyamide fibers are relatively inexpensive and offer a desirable combination of qualities such as durability, comfort, and ease of manufacture into a broad range of colors, patterns, and textures. As a result, polyamide fibers are widely used in the home and industry as carpets, drapery material, upholstery, and clothing. Carpets made from polyamide fibers are a popular floor covering for residential and commercial applications.
Polyamide fibers dye easily with acid dyes. Consequently, carpets made from polyamide fibers stain easily when exposed to natural or artificial acid dyes that exist in some foods, drinks, medicines, and other consumer products. The resulting stains cannot be easily removed under ordinary cleaning conditions. The severe staining of carpeting is a major problem for consumers. In fact, surveys show that more carpets are replaced because of staining than because of wear. Accordingly, it is desirable to provide polyamide fibers that resist common household stains, thereby increasing the life of the carpet.
One way of avoiding such staining is to topically apply to the surface of the polyamide filaments materials that function as stain blockers so as to prevent acid stains from permanently coloring the yarn. Topical treatments may be sulfonated materials that act as "colorless dyes" and bind the amine dye sites on the polyamide polymer. Sulfonated products for topical application to polyamide substrates are described in, for example, U.S. Pat. No. 4,963,409 to Liss et al., U.S. Pat. No. 5,223,340 to Moss, III et al., U.S. Pat. No. 5,316,850 to Sargent et al., and U.S. Pat. No. 5,436,049 to Hu. Topical treatments, however, tend to be costly and non-permanent (wash away with one or more shampoos).
Another way to make stain- or dye-resistant polyamide carpet fibers is to reduce the number of amino end groups in the polyamide yarn. Methods have been developed to reduce the amino end group content of polyamide fibers by adding amino end group blockers such as caprolactone and butyrolactone to the extruder during polymer extrusion. Blocking the end groups during polymer production greatly reduces the rate of polymerization, and the obtainable amino end group level would still be too high to provide meaningful stain resistance.
There remains a need for stain- or dye-resistant polyamide carpet fibers that overcome the above-discussed limitations, as well as a simpler and more economical process for producing the same.
Moreover, during extrusion, polyamides regenerate the starting monomers via the end groups in the melt. The regenerated monomers are deposited on the extruder die, which causes fuming and other processing problems. The regenerated monomers also show up in the finished products.
A need exists, therefore, for a method of reducing the rate of regeneration of starting monomers from polyamides during extrusion.